Copolyamides and compositions based on same

ABSTRACT

The invention concerns copolyamides obtained by using multifunctional monomers. It consists in using a multifunctional monomer comprising at least three reactive functions and at least another multifunctional monomer, in amounts such that the terminal group concentrations are balanced. The copolyamides are particularly high viscosity copolyamides. The invention also concerns compositions based on said copolyamides.

The present invention relates to copolyamides obtained usingmultifunctional monomers. The invention relates more particularly tohigh-viscosity polyamides. The invention also relates to compositionsbased on these copolyamides.

Formed thermoplastic polyamides are used for many applications. Examplesthat may be mentioned include yarns, fibers and filaments, films andarticles obtained by molding, injection-molding or extrusion. Forcertain applications, or for certain forming processes, it isoccasionally preferred to use polyamides with a high melt viscosity.This is the case, for example, for the polyamide fibers used for themanufacture of paper machine felts. This is also the case, for example,for processes for forming articles by extrusion blow-molding. During theimplementation of the latter process, it is generally important for theextruded component not to deform, or to deform only very little underits own weight. The mechanical properties of the material, such as theelastic modulus and the impact strength, must moreover not be affected,or only very little affected.

Several solutions are known for obtaining high-viscosity polyamides. Afirst solution consists in performing a solid-phase postcondensation onlinear polyamides. The postcondensation times are long, which gives riseto high production costs.

Another solution is described in patent application WO 99/03909. Itdescribes copolyamides obtained using a multifunctional monomercomprising a reactive function that forms amide bonds, chosen from acidsand amines, and at least two reactive functions that form amide bonds,which are of different nature and complementary to the previousfunction. These copolyamides have, for an identicalmelt-polycondensation time, a higher melt viscosity than that of linearpolyamides.

However, the copolyamides described in the document have a viscositythat it is sought further to improve. Another object is to achieveequivalent viscosities with shorter and/or controlled polymerizationcycle times.

The object of the invention is to propose novel copolyamides thatespecially have a higher melt viscosity or, for an equivalent viscosity,that may be obtained with shorter polymerization cycles.

To this end, the invention proposes a copolyamide, comprisingmacromolecular units derived from the following monomers:

-   -   (I) at least one difunctional monomer represented by the        abbreviation AB    -   (II) at least one multifunctional monomer represented by the        abbreviation A_(a)B_(b) in which A represents a carboxylic acid        function and B represents an amine function, a and b being        numbers that satisfy the following relationships:        -   a≧1        -   b≧1        -   a+b≧3    -   (III) at least one multifunctional monomer represented by the        abbreviation A_(c)B_(d) in which A represents a carboxylic acid        function and B represents an amine function, c and d being        numbers that satisfy the following relationships:        -   c≧0        -   d≧0        -   c+d≧2, the pair (c,d) being different than the pair (1,1)    -   the monomers (II) and (III) being chosen such that        -   d>c if a>b        -   d<c if a<b    -   the ratio α,        ${\alpha = \frac{{ax} + {cy}}{{ax} + {cy} + {bx} + {dy}}},$    -    being between 0.4 and 0.6,        in which x represents the number of moles of monomer (II) and y        represents the number of moles of monomer (III).

The term “multifunctional monomer” means a monomer comprising at leasttwo reactive functions.

In the present patent application, the abbreviations (AB, A_(a)B_(b) andA_(c)B_(d)) are used to denote organic or organometallic moleculesserving as monomers. The monomers are molecules with reactive functionsof acid type A or of amine type B, capable together of forming amidebonds.

The acid-type functions are advantageously chosen from carboxylic acid,acid halide and ester functions. The amine-type functions areadvantageously chosen from amines, preferably primary amines, and aminesalts.

The number of functions of each type is represented for the variousmonomers by the letters a, b, c and d. The monomers (I) comprise afunction of each type.

The monomers (II) and (III) comprise, respectively, at least 3 and 2functions, and preferably not more than 10. The number of functions foreach (a+b and c+d, respectively) is preferably chosen from 3, 4, 5 and6.

The monomers (II) comprise at least three reactive functions, includingat least one of each type. The monomers (III) comprise at least tworeactive functions, which are either all of the same type, or ofdifferent types. The cases where all the functions are identicalcorrespond to the case where c=0 (monomer comprising only amine-typereactive functions), or to the case where d=0 (monomer comprising onlyacid-type reactive functions). In the case where the monomers (III)comprise functions of different types, the number of functions is thenstrictly greater than two. These conditions are equivalent to thoseexpressed by the equations and inequations presented above.

The number of moles of monomer (II) from which the copolyamide isobtained is denoted by the letter x. The number of moles of monomer(III) from which the copolyamide is obtained is denoted by the letter y.The number of moles of monomer (I) from which the copolyamide isobtained is denoted by the letter z.

The ratio α, $\alpha = \frac{{ax} + {cy}}{{ax} + {cy} + {bx} + {dy}}$is between 0.4 and 0.6 and preferably between 0.45 and 0.55. Even morepreferably, it is substantially equal to 0.5. This condition isequivalent to writing that the number of amine-type functions and thenumber of acid-type functions in the monomers (II) and (III) used toobtain the polymer is relatively, or even substantially totally,equilibrated.

According to one characteristic of the invention, the ratio β,$\beta = \frac{{ax} + {cy} + {bx} + {dy}}{( {a + c + b + d} )*( {x + y + {0.9*z}} )}$is less than 0.05 (5%). It is preferably less than 0.01 (1%) and,according to a very advantageous embodiment, less than 0.002 (0.2%). Theuse of monomers (II) and (III) in larger amounts may lead to copolymerswith very high viscosities and as a result may oblige the use of specialapparatus in order to be able to recover the polymer after it has beenmanufactured. As a guide, and with no limitation to the invention, thefactor 0.9 applied to the number of moles z of the monomer of type ABtakes into account that the monomers (I) generally do not reactentirely. The above ratio is thus close to a ratio between the number ofmoles of monomers (II) and (III) and the number of moles of repeatingunits in the polyamide.

According to another characteristic of the invention, the ratio χ,$\chi = \frac{x + y}{x + y + {0.9*z}}$is preferably less than 0.25%.

The monomers (II) and the monomers (III) may consist, respectively, of amixture of several monomers A_(ai)B_(bi) and A_(cj)B_(dj) in whicha_(i), b_(i), c_(j) and d_(j) satisfy, for at least one of them, theconditions defined above for a, b, c and d with the possible exceptionof the calculation of the ratios α, β and χ, for which the followingapply:${ax} = {\sum\limits_{i}{a_{i}x_{i}\quad\text{for~~the~~calculation~~of~~α~~and~~β}}}$${bx} = {\sum\limits_{i}{a_{i}x_{i}\quad\text{for~~the~~calculation~~of~~α~~and~~β}}}$${cy} = {\sum\limits_{j}{c_{j}y_{j}\quad\text{for~~the~~calculation~~of~~α~~and~~β}}}$${dy} = {\sum\limits_{j}{d_{j}y_{j}\quad\text{for~~the~~calculation~~of~~α~~and~~β}}}$$x = {\sum\limits_{i}{x_{i}\quad\text{for~~the~~calculation~~of~~β~~and~~χ}}}$$y = {\sum\limits_{j}{y_{j}\quad\text{for~~the~~calculation~~of~~β~~and~~χ}}}$in which

-   -   a_(i) represents the number of acid-type functions in a        monomer (II) referenced i    -   b_(i) represents the number of amine-type functions in a        monomer (II) referenced i    -   c_(j) represents the number of acid-type functions in a        monomer (III) referenced j    -   d_(j) represents the number of amine-type functions in a        monomer (III) referenced j    -   x_(i) represents the number of moles of a monomer (II)        referenced i    -   y_(j) represents the number of moles of a monomer (III)        referenced j.

By way of example of systems of monomers (I), (II) and (III) in whichthe monomer (III) is a monomer mixture, mention may be made of systemsin which the monomers (II) and (III) are as follows:

-   -   monomer (II) A_(a)B_(b) with a>b    -   monomers (III): monomer mixture A_(c)B₀ (multifunctional acid),        and A₀B_(d) (multifunctional amine), with c>0 and d>0, and in        amounts such that the ratios α and β are respected.

The monomers (I) are advantageously chosen from:

-   -   ε-caprolactam and/or the corresponding amino acid: aminocaproic        acid, and/or    -   para- or meta-aminobenzoic acid, and/or    -   11-aminoundecanoic acid, and/or    -   lauryllactam and/or the corresponding amino acid:        12-aminododecanoic acid.

More generally, the monomers (I) may be the monomers used to manufacturelinear thermoplastic polyamides. Thus, mention may be made ofω-amino-alkanoic compounds comprising a hydrocarbon-based chaincontaining from 4 to 12 carbon atoms, or the lactams derived from theseamino acids, for instance ε-caprolactam. Mixtures of monomerscorresponding to the abbreviation AB, preferably chosen from themonomers proposed above, may also be used.

The monomers (II) are denoted by the generic term “arborescent”monomers. They may be chosen for the implementation of the inventionfrom the molecules represented by the following formula (b):(XR₁)—R—(R₂Y)_(n)  (b)in which:

-   -   n is an integer greater than or equal to 2 and preferably        between 2 and 10 (limits included) and preferably equal to 2,    -   R₁ and R₂ may be identical or different and represent a covalent        bond or an aliphatic, arylaliphatic, aromatic or alkylaromatic        hydrocarbon-based radical,    -   R is a linear or branched aliphatic radical, a substituted or        unsubstituted cycloaliphatic radical, a substituted or        unsubstituted aromatic radical possibly comprising several        aromatic nuclei and/or hetero ketones    -   X represents an amine or amine salt function, or an acid, ester,        acid halide or amide function    -   Y represents an amine or amine salt function when X represents        an acid, ester, acid halide or amide function, and an acid,        ester, acid halide or amide function when Y represents an amine        or amine salt function.

The monomers (II) that are suitable and preferred according to theinvention are especially the monomers that are heat-stable at atemperature above 150° C. Examples that may be mentioned include themonomers (II) in accordance with the formula presented above in which Rrepresents an aromatic radical such as aminophthalic acid or a linearaliphatic radical such as 3-aminopimelic diacid or 6-aminoundecanedioicacid. Mention may also be made of α-amino acids such as aspartic acidand glutamic acid. Natural amino acids may also be used as monomer (II)if their heat-stability is sufficient. The conditions for synthesizingthe copolyamide may also be adapted as a function of the heat-stabilityof the monomer (II).

Examples of monomers (II) that may be mentioned include:

-   -   5-aminoisophthalic acid,    -   6-aminoundecanedioic acid,    -   3-aminopimelic diacid,    -   aspartic acid,    -   3,5-diaminobenzoic acid,    -   3,4-diaminobenzoic acid,    -   lysine,    -   and mixtures thereof.

According to a first embodiment of the invention, the reactive functionsof the monomer (III) are all identical, chosen from functions of acid oramine type. These monomers are denoted by the generic term “coremonomers”.

A first category of core monomers consists of molecules ormacromolecules (used as monomers) with an arborescent or dendriticstructure. Examples that may be mentioned include polyamines comprisinga high number of amine units. Mention may also be made of the totallyaromatic dendrimers described in patent application WO 95/06081.

A second category of core monomers consists of compounds that may bechosen from the compounds mentioned below.

Mention is made of multifunctional compounds chosen from the compoundsof formula (a)

in which

-   -   C is a covalent bond or an aliphatic hydrocarbon-based radical        that may comprise hetero atoms, and containing from 1 to 20        carbon atoms and preferably from 1 to 6 carbon atoms,    -   X is a radical    -   R₄ is a linear or cyclic, aromatic or aliphatic        hydrocarbon-based radical containing at least two carbon atoms        and possibly comprising hetero atoms,    -   m is an integer between 3 and 8 (limits included).

According to yet another preferred characteristic, the radical R₄ iseither a cycloaliphatic radical such as the tetravalent cyclohexanoylradical, or a 1,1,1-triylpropane or 1,2,3-triylpropane radical.

Examples of other radicals R₄ suitable for the invention that may bementioned include substituted or unsubstituted trivalent phenyl andcyclohexanyl radicals, tetravalent diaminopolymethylene radicals with anumber of methylene groups advantageously between 2 and 12, such as theradical derived from EDTA (ethylenediaminotetraacetic acid), octavalentcyclohexanoyl or cyclohexadinonyl radicals, and radicals derived fromcompounds obtained from the reaction of polyols such as glycol,pentaerythritol, sorbitol or mannitol with acrylonitrile.

Radical A is preferably a methylene or polymethylene radical such as anethyl, propyl or butyl radical, or a polyoxyalkylene radical such as apolyoxyethylene radical.

According to one preferred embodiment of the invention, the number m isgreater than 3 and advantageously equal to 3 or 4.

The reactive function of the multifunctional compound represented by thesymbol X—H is a function capable of forming an amide function.

Examples of multifunctional compounds of formula (a) that may bementioned include 2,2,6,6-tetrakis(β-carboxyethyl)cyclohexanone,diaminopropane-N,N,N′N′-tetraacetic acid of the following formula:

or compounds derived from the reaction of trimethylolpropane or glycerolwith propylene oxide and amination of the hydroxide end groups; thelatter compounds are sold under the trade name Jeffamines T® by thecompany Huntsman, and have the general formula:

in which:

-   -   R₄ represents a 1,1,1-triylpropane or 1,2,3-triylpropane        radical,    -   A represents a polyoxyethylene radical.

Examples of multifunctional compounds that may be suitable areespecially mentioned in document U.S. Pat. No. 5,346,984, in documentU.S. Pat. No. 5,959,069, in document WO 96/35739 and in document EP 672703.

The following may be mentioned more particularly:

nitrilotrialkylamines, in particular nitrilotriethylamine,dialkylenetriamines, in particular diethylenetriamine,trialkylenetetramines and tetraalkylenepentamines, the alkylenepreferably being ethylene, 4-aminoethyl-1,8-octanediamine.

Mention is also made of the dendrimers of formula (II)(R₂—N—(CH₂)_(n))₂—N—(CH₂)_(x)—N—((CH₂)_(n)—NR₂)₂  (II)in which

-   R is a hydrogen atom or a group —(CH₂)_(n)—NR¹ ₂ in which-   R¹ is a hydrogen atom or a group —(CH₂)_(n)—NR² ₂ in which-   R² is a hydrogen atom or a group —(CH₂)_(n)—NR³ ₂ in which-   R³ is a hydrogen atom or a group —(CH₂)_(n)—NH₂,-   n being an integer between 2 and 6,-   x being an integer between 2 and 14,-   N is preferably an integer between 3 and 4, in particular 3, and x    is preferably an integer between 2 and 6, preferably between 2 and 4    (limits included), in particular 2. Each radical R may be chosen    independently of the others. The radical R is preferably a hydrogen    atom or a group —(CH₂)_(n)—NH2.

Mention is also made of multifunctional compounds containing 3 to 10carboxylic acid groups, preferably 3 or 4. Among these, the ones thatare preferred are the compounds containing an aromatic and/orheterocyclic ring, for example benzyl, naphthyl, anthracenyl, biphenyland triphenyl radicals, or heterocycles, for instance pyridine,bipyridine, pyrrole, indole, furan, thiophene, purine, quinoline,phenanthrene, porphyrin, phthalocyanine and naphthalocyanine.3,5,3′,5′-Biphenyltetracarboxylic acid, acids derived fromphthalocyanine and from naphthalocyanine,3,5,3′,5′-biphenyltetracarboxylic acid,1,3,5,7-naphthalenetetracarboxylic acid, 2,4,6-pyridinetricarboxylicacid, 3,5,3′,5′-bipyridyltetracarboxylic acid,3,5,3′,5′-benzophenonetetracarboxylic acid and1,3,6,8-acridinetetracarboxylic acid are most particularly preferred,and even more particularly trimesic acid and1,2,4,5-benzenetetracarboxylic acid.

Mention is also made of multifunctional compounds whose core is aheterocycle containing a point of symmetry, for instance1,3,5-triazines, 1,4-diazines, melamine, compounds derived from2,3,5,6-tetraethylpiperazine, 1,4-piperazines and tetrathiafulvalenes.Mention is made more particularly of1,3,5-triazine-2,4,6-triaminocaproic acid (TTAC).

According to another embodiment, the monomers (III) are arborescentmonomers that may be chosen from those mentioned as monomers (II), itbeing understood that:

-   -   they are of different nature    -   the conditions regarding the number of functions are satisfied.

More generally, the choice of monomers (II) and (III) must firstlysatisfy the conditions regarding the numbers of functions of each type(symbolized by the letters a, b, c and d). Certain combinations of themonomers (II) and (III) mentioned above are therefore not in accordancewith the invention.

According to one particularly advantageous embodiment, the copolyamideis obtained from systems of monomers (I), (II) and (III), of which themonomers (II) and (III) are chosen from the following systems:

-   -   system 1: monomer (II) AB₂ and monomer (III) A₃ or A₄    -   system 2: monomer (II) A₂B and monomer (III) B₃ or B₄.

According to one preferred embodiment, no monofunctional monomer is usedin addition to the monomers (I), (II) or (III).

In order to be able to perform the polymerization under the bestpossible conditions, monomers with a sufficient heat stability are mostparticularly preferred for the monomers (I), (II) and (III).

According to one advantageous characteristic, the melt flow index of thecopolyamides, measured at 275° C. under 5 kg of pressure, is less than10 g/10 minutes.

The invention also relates to compositions comprising the copolyamidedescribed above. The compositions may comprise at least one polyamide inaccordance with the invention and optionally other additives such asmolding or mold-stripping agents, heat-stabilizers, light-stabilizers,antioxidants, flame retardants, pigments, colorants and lubricants. Thecomposition may also comprise agents for improving the impact strengthand/or bulking or reinforcing fillers. Mention is made in particular ofglass fibers.

The compositions of the invention may also comprise as polymer matrix,in addition to the polyamide as described above, other thermoplasticmaterials such as linear aliphatic polyamides, optionallycompatibilized, or aromatic or semiaromatic polyamides, for example.

According to one characteristic of the invention, the compositions ofthe invention are obtained by blending, generally in a single-screw ortwin-screw extruder, a polyamide in accordance with the invention withthe various additives, this blending generally being performed with thepolyamide melt, followed by extrusion of the blend in the form of rodsthat are then chopped into granules. Molded parts may then be made bymelting the granules produced above and feeding the composition meltinto suitable molding, injection-molding or extrusion devices.

A subject of the invention is also a process for manufacturing acopolyamide in accordance with the invention.

In a first embodiment of this manufacturing process, a mixture ofmonomers is prepared with determined proportions of each component. Saidmixture is polymerized under conditions and according to a procedureequivalent to those used for the manufacture of the linear polyamidecorresponding to the difunctional monomers used. Thus, whenε-caprolactam is used, water is added to the mixture of monomers toinitiate the hydrolytic opening of the caprolactam.

According to a second embodiment of the invention, a linear polyamideprepolymer is manufactured by polycondensation of the monomers (I) toobtain a prepolymer with a number-average molecular weight {overscore(Mn)} of the order of 2 000 to 3 000 approximately.

The monomers (II) and (III) are added to the linear prepolymer and thepolymerization is continued either in molten medium or in solid phase.The solid-phase production method makes it possible especially to obtaincopolyamides using multifunctional monomers that show heat stability atrelatively low temperatures, for example below 200° C., since thesolid-phase postcondensation temperature is reached at lowertemperatures than those for polymerization in molten medium.

The addition of the monomers (II) and (III) may be performed in theextruder or in a reactor, the solid-phase postcondensation being carriedout according to the standard conditions usually used for that of linearpolyamides.

According to another variant of this embodiment of the process formanufacturing a copolyamide in accordance with the invention, themonomers (II) and (III) are added with a catalyst, thus making itpossible to perform the reaction directly in the extruder. The catalyststhat are suitable are the catalysts conventionally used for amidation orpolycondensation reactions of amide functions, for example such asphosphorus-based compounds.

The invention also relates to a process for manufacturing novelcopolyamides or novel compositions by extrusion, and to the copolyamidesor compositions obtained by the process. This process usesmultifunctional compounds, under conditions similar to those describedabove, and lead to macromolecular compounds or compositions whosecharacteristics are similar if not identical to those of thecopolyamides and compositions described above.

A process is thus proposed for the manufacture of a copolyamide or acomposition comprising a copolyamide, which consists in mixing in anextrusion device at least the following three compounds:

-   -   compound (I): a polyamide containing repeating units of        formula (c) below:        —[NH—R₃—CO]—  (c)    -   compound (II): monomer (II) as defined above    -   compound (III): monomer (III) as defined above        the ratio α,        ${\alpha = \frac{{ax} + {cy}}{{ax} + {cy} + {bx} + {dy}}},$        being between 0.4 and 0.6,

in which x represents the number of moles of compound (II) and yrepresents the number of moles of compound (III)the ratio β,$\beta = \frac{{ax} + {cy} + {bx} + {dy}}{( {a + c + b + d} )*( {x + y + z} )}$being less than 1% and preferably 0.5%,

in which z represents the number of moles of repeating units in compound(I)

the radical R₁ being a hydrocarbon-based radical optionally comprisinghetero atoms.

z is defined in the following manner:

z=m_(D)/M_(D) in which m_(D) is the mass of compound (I) used and M_(D)is the molar mass of a repeating unit.

The ratio $\alpha = \frac{{ax} + {cy}}{{ax} + {cy} + {bx} + {dy}}$is preferably between 0.45 and 0.55. Even more preferably, it issubstantially equal to 0.5.

The ratio $\chi = \frac{x + y}{x + y + z}$is preferably less than 0.5%.

Compound (I) is preferably chosen from polyamide 6, polyamide 11,polyamide 12 and blends and copolymers based on these polyamides.

The process may comprise the introduction of fillers or additives asmentioned above. Glass fiber is most particularly mentioned.

The copolyamides or compositions according to the invention may be usedin many applications, such as the manufacture of molded orinjection-molded parts.

They are especially suitable for manufacturing parts by extrusionblow-molding techniques. Specifically, the low melt flow index of thecopolyamide makes it possible to limit the deformations of the parisonsduring their extrusion, before the blow-molding step.

It is also possible to manufacture articles by injection-moldingprocesses using the copolyamides of the invention. These articles havemechanical properties that are markedly higher than those of thearticles obtained by injection-molding of a linear polyamide-basedcomposition of the same melt flow index.

Other details or advantages of the invention will emerge more clearly inthe light of the examples given below, purely for indicative purposes.

The following monomers are used:

-   -   CL: caprolactam    -   AIA: 5-aminoisophthalic acid    -   DAB: 2,5-diaminobenzoic acid    -   J3: Jeffamine T 403, sold by the company Huntsman (triamine core        monomer)    -   T4: 2,2,6,6-tetrakis(β-carboxyethyl)cyclohexanone (tetraacid        core monomer).

The copolyamides are synthesized according to one of the two cyclesbelow:

Cycle 1:

11.3 kg of caprolactam, 300 g of water and various amounts of themonomers mentioned above are mixed together in an autoclave equippedwith heating and stirring means. The mixture is heated for 4 hours untila pressure of 3-6 bar is reached, the pressure is reduced over two hoursdown to a pressure of 0.2 bar, with an internal vacuum the pressure isreduced to 400 mm/Hg over two hours, and this pressure is maintained for30-60 minutes. The polymer obtained is extruded under nitrogen pressure(4 to 6 bar).

Cycle 2:

Polymerization in an autoclave for 10 hours at atmospheric pressure, at275° C., with circulation of nitrogen.

The characteristics and properties of the copolyamides evaluated are asfollows:

-   -   melt flow index (MFI): evaluated according to standard ISO 1133        at 275° C. under 5 kg of pressure.    -   relative viscosity (RV): evaluated in 96% sulfuric acid        solution, according to standard ISO 307,    -   NH₂ and COOH end groups: evaluated by potentiometric analysis.        Expressed as meq/kg of polymer,    -   mechanical properties:        -   impact: notched IZOD impact strength, measured at 23° C.            under 50% relative humidity, on dry material, according to            standard ISO 180/1A.        -   modulus, elongation, yield stress: measured at 23° C. under            50% relative humidity, on dry material, according to            standard ISO 527.

EXAMPLES 1 TO 16

Various copolyamides are synthesized, the characteristics of which aregiven in table I. The nature of the monomers (II) and (III) used, andthe amount in molar percentage (respective ratios$\frac{x}{x + y + {0.9*z}}\quad\text{and}\quad\frac{y}{x + y + {0.9*z}}$are specified for each copolyamide. Monomer (I) is caprolactam.

TABLE I Monomer (II) Monomer (III) Example (nature, mol %) (nature, mol%) Cycle  1 DAB; 0.004 T4; 0.001 1  2 DAB; 0.008 T4; 0.002 1  3 DAB;0.024 T4; 0.006 1  4 DAB; 0.04 T4; 0.01 1  5 DAB; 0.12 T4; 0.03 1  6DAB; 0.16 T4; 0.04 1  7 AIA; 0.1125 J3; 0.0375 1  8 DAB; 0.075 AIA;0.075 1  9 (comparative) / / 1 10 (comparative) AIA; 0.15 / 1 11(comparative) DAB; 0.15 / 1 12 (comparative) / / 2 13 AIA; 0.15 / 2 14AIA; 0.1125 J3; 0.0375 2 15 (comparative) DAB; 0.15 / 2 16 DAB; 0.12 T4;0.03 2

The characteristics and properties are given in table II.

TABLE II Example MFI (g/10 min) VR NH₂ (meq/kg) COOH (meq/kg) 1 30 3.4537.1 37.9 2 27 3.49 36.8 37.3 3 19 3.58 34.4 35.5 4 12 3.78 32.7 34.6 56 4.22 29.3 31.7 6 <3.5 >4.3* 27.2 29.9 7 8.5 3.87 33.1 29.5 8 10.5 3.9730.8 32.4 9 34 3.21 42.4 41.4 10 22 3.41 22.7 45.5 11 18 3.5 51.3 24.212 15 3.89 30.9 31.9 13 4.5 4.55 27 54 14 2.1 5.46 25.5 21 15 5.2 4.7234.8 19.7 16 1.7 5.73 22.5 20.6

The mechanical properties of certain polymers are given in table III.

TABLE III Impact Elongation Yield stress Polymer (kJ/m²) Modulus (N/mm²)(%) (N/mm²) Example 9 5.2 2610 70 46.2 PA 6 VR 4 5.7 2780 90 46.7Example 10 4.9 2638 85 49.1 Example 1 5.5 2990 71 47 Example 5 5.7 299090 48

EXAMPLE 17

A solid-phase postcondensation is carried out, at 175° C., undernitrogen, on a copolyamide according to example 1 and a linear polyamide6 according to example 9, respectively. The relative viscosity of thepolymers is measured every two hours.

A BRIEF DESCRIPTION OF THE DRAWINGS

The curves representing the change are given in FIG. 1, with the time inhours on the y-axis and the relative viscosity on the x-axis.

It is observed that the relative viscosity does not vary for thecopolyamides according to the invention. The molecular mass of thecopolyamides according to the invention is thus easy to control.

EXAMPLE 18

The rheological properties of various polyamides and copolyamides areevaluated, at different shears. A GOETTFRERT WinRHEO V 3.22 capillaryrheometer is used to do this; at a temperature of 250° C., and pressuresof 65 to 1 200 bar. These measurements are performed on the followingpolymers, respectively:

-   -   copolyamide according to example 5    -   polyamide 6 of relative viscosity 4 (PA 6 RV 4)    -   polyamide 6 of relative viscosity 5 (PA 6 RV 5).

The curves representing the melt viscosity (Pa.s) as a function of theshear (s⁻¹) are given in FIG. 2.

It is observed that the difference in rheological behavior between acopolyamide according to the invention and a linear polyamide is morepronounced at low shear than at high shear. This makes the copolyamidesaccording to the invention particularly advantageous, especially forextrusion processes. They show good processability in an extruder (highshear) and also a high viscosity at low shear, after extrusion, for ablow-molding operation.

EXAMPLE 20

Bottles are manufactured by extrusion blow-molding using a Comec MS 1000machine, under the following conditions:

-   -   temperature profile in the extruder (° C.): 220, 230, 235, 235,        240, 240, 240, 235    -   pressure: 200 bar    -   screw: 40 rpm    -   blow-molding pressure: 4 bar    -   blow-molding time: 8 seconds    -   cycle time: 16 seconds    -   polymer used: example 5.

The weight of the bottles obtained is 115±10 g. The walls have aconstant and uniform thickness, with excellent surface aspect.

1. A copolyamide, comprising macromolecular units derived from thefollowing monomers: (I) at least one difunctional monomer represented bythe abbreviation AB (II) at least one multifunctional monomerrepresented by the abbreviation AaBb in which A represents a carboxylicacid function and B represents an amine function, a and b being numbersthat satisfy the following relationships: a≧1 b≧1 a+b≧3 (III) at leastone multifunctional monomer represented by the abbreviation AcBd inwhich A represents a carboxylic acid function and B represents an aminefunction, c and d being numbers that satisfy the followingrelationships: c≧0 d≧0 c+d≧2, the pair (c,d) being different than thepair (1,1) the monomers (II) and (III) being chosen such that d>c if a>bd<c if a<b the ratio $\frac{{ax} + {cy}}{{ax} + {cy} + {bx} + {dy}}$ being between 0.4 and 0.6, in which x represents the number of moles ofmonomer (II) and y represents the number of moles of monomer (III) theratio$\frac{{ax} + {cy} + {bx} + {dy}}{( {a + c + b + d} )*( {x + y + {0.9*z}} )}$ is less than 0.05, in which z represents the number of moles of monomer(I).
 2. The copolyamide as claimed in claim 1, wherein the ratio$\frac{{ax} + {cy} + {bx} + {dy}}{( {a + c + b + d} )*( {x + y + {0.9*z}} )}$is less than 0.01, in which z represents the number of moles of monomer(I).
 3. The copolyamide as claimed in claim 2, wherein the ratio$\frac{{ax} + {cy} + {bx} + {dy}}{( {a + c + b + d} )*( {x + y + {0.9*z}} )}$is less than 0.002.
 4. The copolyamide as claimed in claim 1, whereinthe ratio $\chi = \frac{x + y}{x + y + {0.9*z}}$ is less than 0.25%. 5.The copolyamide as claimed in claim 1, wherein integers a, b, c and dare chosen so as to satisfy one of the following series ofrelationships: a>b, c=0, d≧3 a>b, d=0, c≧3.
 6. The copolyamide asclaimed in claim 1, wherein a=1, b=2, c=4 and d=0.
 7. The copolyamide asclaimed in claim 1, wherein the melt flow index, measured at 275° C.under a 5 kg load, is less than 10 g/10 minutes.
 8. The copolyamide asclaimed in claim 1, wherein the monomer (I) is a lactam, an amino acidor a mixture of these compounds.
 9. The copolyamide as claimed in claim1, wherein the monomer (I) is elected from the group consisting ofcaprolactam and aminocaproic acid, and mixtures thereof.
 10. Thecopolyamide as claimed in claim 1, wherein monomer (II) is representedby formula (b): (XR₁)—R—(R₂Y)_(n) (b) in which: n is an integer greaterthan or equal to 2, limits included, R₁ and R₂ may be identical ordifferent and represent a covalent bond or an aliphatic, arylaliphatic,aromatic or alkylaromatic hydrocarbon radical, R is a linear or branchedaliphatic radical, a substituted or unsubstituted cycloaliphaticradical, a substituted or unsubstituted aromatic radical optionallycomprising several aromatic nuclei and/or hetero ketones X represents anamine or amine salt function, or an acid, ester, acid halide or amidefunction Y represents an amine or amine salt function when X representsan acid, ester, acid halide or amide function, and an acid, ester, acidhalide or amide function when Y represents an amine or amine saltfunction.
 11. The copolyamide as claimed in claim 1, wherein the monomer(III) is represented by formula (a)

in which C is a covalent bond or an aliphatic hydrocarbon radicaloptionally comprising hetero atoms, and containing from 1 to 20 carbonatoms, X is a radical

R₄ is a linear or cyclic, aromatic or aliphatic hydrocarbon radicalcontaining at least two carbon atoms and optionally comprising heteroatoms, m is an integer between 3 and 8, limits included.
 12. Thecopolyamide as claimed in claim 11, wherein the multifunctional compoundis selected from the group consisting of2,2,6,6-tetrakis(β-carboxyethyl)cyclo-hexanone, trimesic acid,2,4,6-tris(aminocaproic acid)-1,3,5-triazine and4-aminoethyl-1,8-octanediamine.
 13. The copolyamide as claimed in claim1, which is obtained by mixing, in an extrusion device, at least thefollowing three compounds: compound (I): a polyamide containingrepeating units of formula (c) below: —(NH—R₃—CO]— (c) compound (II):monomer (II) as defined above compound (III): monomer (III) as definedabove the ratio α,${\alpha = \frac{{ax} + {cy}}{{ax} + {cy} + {bx} + {dy}}},$  beingbetween 0.4 and 0.6, in which x represents the number of moles ofcompound (II) and y represents the number of moles of compound (III) theratio β,$\beta = \frac{{ax} + {cy} + {bx} + {dy}}{( {a + c + b + d} )*( {x + y + z} )}$ being less than 1%, in which z represents the number of moles ofrepeating units in compound (I) the radical R₁ being a hydrocarbonradical optionally comprising hetero atoms.
 14. A composition comprisinga copolyamide matrix and a reinforcing filler, wherein the matrixcomprises a copolyamide as claimed in claim
 1. 15. A yarn, fiber,filament, molded or injection-molded article, or film comprising acopolyamide or a composition as claimed in claim
 1. 16. An articleobtained by extrusion blowmolding of a polyamide or a composition asclaimed in claim
 1. 17. The copolyamide as claimed in claim 10, whereinn is an integer between 2 and 10 (limits included).
 18. The copolyamideas claimed in claim 10, wherein n is equal to
 2. 19. The copolyamide asclaimed in claim 11, wherein C is an aliphatic hydrocarbon radicaloptionally comprising heteroatoms and containing 1-6 carbon atoms.